Wireless local area network system, fault recovery method, and recording medium stored therein a computer program executing the fault recovery process

ABSTRACT

The present invention provides a wireless local area network (LAN) system preventing throughput from being decreased even when a fault occurs in an access point, a fault recovery method, and a recording medium stored therein a computer program for executing the fault recovering process. The method for use in a wireless local area network system comprising a plurality of access points and a plurality of client terminals, the method comprising the steps of: detecting, by each of the access points, whether a fault occurs on each of the access points itself; disconnecting, by the access point which has detected the fault, the client terminal connected thereto; searching for, by the disconnected client terminal, another of the client terminals to which the disconnected client terminal is to be connected; and connecting the disconnected client terminal to the searched client terminal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless local area network (LAN)system, a fault recovery method, and a recording medium stored therein acomputer program or executing the fault recovering process. Moreparticularly, the present invention relates to a technology forpreventing the throughput of the whole LAN system from being decreasedeven when a fault occurs in an access point.

2. Description of the Prior Art

Conventionally, there has been a wireless local area network (LAN)system connected to a wired LAN and many wireless terminals.

Japanese Patent Laid-Open Publication No. Hei 7-312597 (disclosed inJapan on Nov. 28, 1995) discloses a wireless LAN system that preventspackets from being lost. This technology will be described below as afirst conventional example.

FIG. 10 is a block diagram showing the wireless LAN system according tothe first conventional example. A wireless LAN system 110, shown in FIG.10, consists of a client terminal 18 connected to a wired LAN 112, a LANcable 120 forming the wired LAN 112, access points 122 and 124performing as bridges to the wired LAN 112, and wireless terminals 130and 134 which, in conjunction with the access points 122 and 124, formwireless LANs 114 and 116, respectively.

In the system of this conventional example, when the source wirelessterminal 130 transmits a packet to the destination wireless terminal 134but the wireless terminal 134 does not respond to it, the access point122 or 124 transmits the packet to the wireless LAN 114 or 116 ortransmits the packet to the wired LAN 112. In this way, the systemprevents a packet loss caused by a conflict in accessing the medium oran interference with other communication networks using the samefrequency band.

Japanese Patent Laid-Open Publication No. Hei 8-242232 (disclosed inJapan on Sep. 17, 1996) discloses a wireless terminal LAN having arepeater. This technology will be described as a second conventionalexample.

FIG. 11 is a block diagram of the wireless LAN system of the secondconventional example. The wireless terminal LAN, shown in FIG. 11,consists of wireless terminals 202-210 and a wireless repeater 201containing a transceiver 220.

The system according to this conventional example has the specialwireless repeater 201 and, through this wireless repeater 201,re-transmits packets to reduce conflicts in radio waves. Thus, thesystem can prevent the throughput of the whole LAN from being decreased.

Japanese Patent Laid-Open Publication No. Hei 9-215044 (disclosed inJapan on Aug. 15, 1997) discloses a priority switching technology for acellular wireless LAN. This technology will be described as a thirdconventional example.

FIG. 12 is a block diagram of the wireless LAN system according to thethird conventional example. The wireless LAN system, shown in FIG. 12,consists of a plurality of portable units 302 that are wirelessterminals, a house computer 304 connected to a wired LAN, and aplurality of access points 305 that perform as bridges to the wired LAN.

In the system according to this conventional example, the portable unit302 searches and identifies the access point 305 best suited forcommunication, based on the intensity of radio waves from, and theloading factor of, the plurality of the access points 305.

In addition, to make the advantages of the present invention clearer, avirtual technology with a configuration equivalent to that of the systemaccording to the present invention will be described as a fourthconventional example.

FIG. 13 is a block diagram of a wireless LAN system according to thefourth conventional example. FIG. 14 is a flowchart showing a faultrecovery processing of the wireless LAN system according to the fourthconventional example.

The wireless LAN system, shown in FIG. 13, consists of access points Paand Pb that perform as bridges to a wired LAN system Lw, clientterminals Ca-Cd that are wireless terminals communicating with theaccess points Pa and Pb, and a LAN cable 405 consisting the wired LANsystem Lw.

As shown in FIG. 13, the access points Pa and Pb transmit beaconinformation Iba and Ibb, respectively, at regular intervals (step S101in FIG. 14).

When the client terminal Ca receives the beacon information Iba from theaccess point Pa at power-on time or roaming time, the client terminal Catransmits a management frame back to the access point Pa to startnegotiation with the access point Pa and then starts communication withthe access point Pa.

The client terminal Cb also starts negotiation with the access point Pband then starts communication with the access point Pb according to thesame procedure (step S102 in FIG. 14).

At this point, when the access point Pa fails for some reason or other(step S103 in FIG. 14), the client terminal Ca cannot continuecommunication with the access point Pa. So, the client terminal Castarts searching for another access point Pb (step S104 in FIG. 14).

If another access point Pb is near the client terminal Ca (step S105 inFIG. 14), there is no problem because the client terminal Ca canimmediately establish a link with the access point Pb to continuecommunication (step S106 in FIG. 14).

However, if another access point Pb is not near the client terminal Ca(step S105 in FIG. 14), the client terminal Ca continues searchprocessing until it successfully searches for the access point Pb (stepS104 in FIG. 14).

This search processing is executed by the client terminal Ca fortransmitting a management frame (probe) that is communication controlmanagement information. To establish the link to the access point Pb assoon as possible and to continue communication reliably, the clientterminal Ca continues transmitting the management frame, during thissearch processing, at an interval shorter than that for a normalcommunication frame.

However, the above processing has the problems described below.

First, in the above search processing, the client terminal Ca frequentlytransmits the management frame at an interval shorter than that for thenormal communication frame. This increases the radio wave interferencearound the client terminal Ca and therefore decreases the throughput ofthe whole LAN system L.

Second, in the above search processing, the client terminal Cafrequently transmits the management frame at an interval shorter thanthat for the normal communication frame. This processing has someproblems with the client terminal Ca being battery-powered. For example,this processing consumes more battery power for communication andtherefore shortens battery life. And, the increase in power consumptioncauses a quickly decrease in the power voltage, sometimes suddenlydisconnecting the power of the portable information terminal and thusdestroying data due to a communication interruption.

Third, in a wireless LAN system Ll, the duplicated system configurationis built usually for the access points Pa and Pb as a fail-safe againstthe shutdown of the whole LAN system L. This shutdown may be caused bysuch conditions as a fault in access point Pa or Pb or the disconnectionof a LAN cable 405. However, in a wireless LAN system used generally inJapan, whose frequency bandwidth is only one third of a wireless LANsystem generally used in the United States, duplicating the accesspoints Pa and Pb allows the access points Pa and Pb to transmit radiowaves frequently during the above search processing. This increases theradio wave interference and therefore decreases the throughput of thewhole LAN system.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a wireless LAN systemthat prevents throughput from being decreased even when an access pointfails, a fault recovery method, and a recording medium storing therein acomputer program executing the fault recovery process.

The wireless LAN (Local Area Network) system according to the presentinvention consisting of a plurality of access points and a plurality ofclient terminals; wherein each of the plurality of access pointsconsists of: a main unit for communicating with the client terminals, afirst fault detecting unit for detecting a fault on the main unit, and adisconnection controlling unit for disconnecting the client terminalconnected to the access point where the fault was detected by the firstfault detecting unit; and wherein each of the plurality of clientterminals consists of: a transceiver unit for communicating with theaccess point, a search controlling unit for searching for another clientterminal to which the client terminal disconnected from the access pointis to be connected, and a connection controlling unit for connecting thedisconnected client terminal to the searched client terminal by thesearch controlling unit.

The fault recovery method according to the present invention consistingof a plurality of access points and a plurality of client terminals, themethod consisting of the steps of: detecting, by each of the accesspoints, whether a fault occurs on each of the access points itself;disconnecting, by the access point which has detected the fault, theclient terminal connected thereto; searching for, by the disconnectedclient terminal, another of the client terminals to which thedisconnected client terminal is to be connected; and connecting thedisconnected client terminal to the searched client terminal.

The recording medium stores therein a computer program for executing afault recovery process according to the present invention consisting ofa plurality of access points and a plurality of client terminals, theprocess consisting of the steps of: detecting, by each of the accesspoints, whether a fault occurs on each of the access points itself;disconnecting, by the access point which has detected the fault, theclient terminal connected thereto; searching for, by the disconnectedclient terminal, another of the client terminals to which thedisconnected client terminal is to be connected; and connecting thedisconnected client terminal to the searched client terminal.

When a fault occurs in an access point, a client terminal connected tothis access point is disconnected. Instead of connecting thedisconnected client terminal to another access point as in theconventional example, the system according to the present inventionconnects the client terminal to another client terminal. And, throughthis another client terminal, the disconnected client terminal connectsto another access point. This prevents the load from being concentratedat another access point.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a wireless LAN system in an embodimentof the present invention.

FIG. 2 is a block diagram of an access point of the wireless LAN systemaccording to the FIG. 1 embodiment.

FIG. 3 is a block diagram of a client terminal of the wireless LANsystem according to the FIG. 1 embodiment.

FIG. 4 is a flowchart showing a fault recovery processing of thewireless LAN system according to the FIG. 1 embodiment.

FIG. 5 is a diagram showing communication processing in the normal stateof the wireless LAN system according to the FIG. 1 embodiment.

FIG. 6 is a diagram showing disconnection processing in the faultoccurring state of the wireless LAN system according to the FIG. 1embodiment.

FIG. 7 is a diagram showing search processing in the fault occurringstate the wireless LAN system according to the FIG. 1 embodiment.

FIG. 8 is a diagram showing connection processing in the fault occurringstate of the wireless LAN system according to the FIG. 1 embodiment.

FIG. 9 is a diagram showing another connection processing in the faultoccurring state of the wireless LAN system according to the FIG. 1embodiment.

FIG. 10 is a block diagram of the wireless LAN system according to thefirst conventional example.

FIG. 11 is a block diagram of the wireless LAN system according to thesecond conventional example.

FIG. 12 is a block diagram of the wireless LAN system according to thethird conventional example.

FIG. 13 is a block diagram of the wireless LAN system according to thefourth conventional example.

FIG. 14 is a flowchart showing a fault recovery processing of thewireless LAN system according to the fourth conventional example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a block diagram showing a wireless LAN system in an embodimentof the present invention.

A wireless LAN system Ll, shown in FIG. 1, consists of access points Paand Pb that are bridges to a wired LAN system Lw and client terminalsCa-Cd that are wireless communication terminals communicating with theseaccess points Pa and Pb.

This wireless LAN system Ll uses Carrier Sense Multiple Access withCollision Avoidance (CSMA/CA) as the communication protocol. Note thatany number of the access points Pa and Pb and the client terminals Ca-Cdmay be used.

On the other hand, the wired LAN system Lw consists of the access pointsPa and Pb, which are bridges to the wireless LAN system Ll, and a LANcable 5 which is, for example, an Ethernet cable connecting the accesspoints Pa and Pb. This wired LAN system Lw uses Carrier Sense MultipleAccess with Collision Detection (CSMA/CD) as the communication protocol.

FIG. 2 is a block diagram of an access point of the wireless LAN systemaccording to the FIG. 1 embodiment. The access point Pa, shown in FIG.2, consists of a main unit 1 a, a fault detecting unit 10 a, adisconnection controlling unit 20 a, a fault detecting unit 30 a, and apermission information generating unit 40 a.

The main unit 1 a is a relaying unit connecting the wired LAN system Lw(FIG. 1) and the wireless LAN system Ll (FIG. 1). The main unit 1 acommunicates with the client terminals Ca and Cb (FIG. 1) included in anarea Aa (FIG. 1) served by the access point Pa by radio waves. Not onlythe radio waves but also other wireless communication media such as aninfrared ray may be used as the communication medium.

In addition, the main unit 1 a transmits management information, calledbeacon information Iba (FIG. 1), at regular intervals. The beaconinformation is composed of synchronization information, packettransmission control information, and so on. By exchanging the beaconinformation Iba and Ibb (FIG. 1) with the other access point Pb, themain unit 1 a maintains the synchronization of the whole LAN system and,at the same time, controls communication so that a packet collision isavoided.

The fault detecting unit 10 a is means for monitoring the status ofcommunication between the wired LAN system Lw and the main unit 1 a.When the main unit 1 a of the access point Pa fails or the LAN cable 5is disconnected, the fault detecting unit 10 a detects that the mainunit 1 a has been disconnected from the LAN cable 5 and outputs a faultdetecting signal Sha.

In response to the fault detecting signal Sha, the disconnectioncontrolling unit 20 a outputs a disconnect signal Sda to the main unit 1a to instruct the main unit 1 a to disconnect the client terminal Ca(FIG. 1) being connected.

The fault detecting unit 30 a receives the beacon information Ibb(FIG. 1) from the other access point Pb (FIG. 1). If the fault detectingunit 30 a detects that the other access point Pb (FIG. 1) has failed,the fault detecting unit 30 a outputs a fault detecting signal Spa.

In response to the fault detecting signal Spa, the permissioninformation generating unit 40 a transmits permission information Ipwhich permits all the client terminals under control of the access pointPa, that is, Ca and Cb (FIG. 1), to accept the urgent identification(ID) code.

A main unit 1 b, a fault detecting unit 10 b, a disconnectioncontrolling unit 20 b, a fault detecting unit 30 b, and a permissioninformation generating unit 40 b of the access point Pb each have theconfiguration similar to that of the corresponding unit of the accesspoint Pa.

FIG. 3 is a block diagram of a client terminal of the wireless LANsystem according to the FIG. 1 embodiment. The client terminal Ca shownin FIG. 3 consists of a transceiver unit 50 a, a search controlling unit60 a, a connection controlling unit 70 a, and a repeat controlling unit80 a.

The transceiver unit 50 a communicates with the access points Pa and Pb(FIG. 1) by radio waves.

When communication is forced to terminate by the access point Pa or Pb,the search controlling unit 60 a transmits a management frame throughthe transceiver unit 50 a to search for another client terminal Cb-Cd towhich the client terminal Ca will be connected.

The connection controlling unit 70 a connects the client terminal Ca,through the transceiver unit 50 a, to one of the client terminals Cb-Cdthat was searched for by the search controlling unit 60 a.

When a connection request is received from the connection controllingunit 70 b-70 d of one of the other client terminals Cb-Cd, the repeatcontrolling unit 80 a instructs the transceiver unit 50 a to performcommunication processing for the MAC (Media Access Control) sub-layerand lower-level layers for data to be communicated between one of theclient terminals Cb-Cd and the access point Pa or Pb (FIG. 1).

Transceiver units 50 b-50 d, search controlling units 60 b-60 d,connection controlling units 70 b-70 d, and repeat controlling units 80b-80 d of the client terminals Cb-Cd each have the configuration similarto that of client terminal Ca.

The client terminals Ca-Cd may be, for example, standalone computers,POS (Point-Of-Sales) terminals, or portable information terminals withthe radio communication function, or computers, POS terminals, orportable information terminals with no radio communication function butwith a radio communication adapter connected.

FIG. 4 is a flowchart showing a fault recovery processing of thewireless LAN system according to the FIG. 1 embodiment.

As shown in FIG. 1, the access points Pa and Pb transmit the beaconinformation Iba and Ibb at regular intervals, respectively (step S1 inFIG. 4).

FIG. 5 is a diagram showing communication processing in the normal stateof the wireless LAN system according to the FIG. 1 embodiment. Uponreceiving the beacon information Iba from the access point Pa atpower-on time or roaming time, the client terminal Ca transmits themanagement frame back to the access point Pa to perform negotiationtherewith. The client terminal Ca then starts communication with theaccess point Pa as shown in FIG. 5 (step S2 in FIG. 4).

Each of the client terminals Cb-Cd performs negotiation with the accesspoint Pb in the same way as described above and, as shown in FIG. 5,starts communication with the access point Pb.

Because this negotiation processing is a basic wireless LAN systemtechnology that is well known, its description is omitted here.

FIG. 6 is a diagram showing disconnection processing in the faultoccurring state the wireless LAN system according to the FIG. 1embodiment. Assume that, during normal communication processing shown inFIG. 5, a fault occurs on the access point Pa as shown in FIG. 6 (stepS3 in FIG. 4). The cause of this fault is, for example, a fault in themain unit 1 a (FIG. 2) of the access point Pa or the disconnection ofthe LAN cable 5 connected to the main unit 1 a (FIG. 2).

The fault detecting unit 10 a (FIG. 2) of the access point Pa monitorsthe status of communication between the wired LAN system Lw and the mainunit 1 a (FIG. 2). When the fault detecting unit 10 a detects a fault onthe main unit 1 a of the access point Pa or on the LAN cable 5 connectedtherewith, the fault detecting unit 10 a (FIG. 2) outputs the faultdetection signal Sha (FIG. 2) to the disconnection controlling unit 20 a(FIG. 2). In response to the fault detection signal Sha (FIG. 2), thedisconnection controlling unit 20 a (FIG. 2) disconnects the clientterminal Ca, which is connected to the access point Pa at that time,from the access point Pa and forces communication between them toterminate (step S4 in FIG. 4).

FIG. 7 is a diagram showing search processing in the fault occurringstate of the wireless LAN system according to the FIG. 1 embodiment. Asshown in FIG. 7, the search controlling unit 60 a (FIG. 3) of thedisconnected client terminal Ca transmits a management frame, which ismanagement information, through the transceiver unit 50 a (FIG. 3) tosearch for another client terminal Cb-Cd to which the client terminal Cais to be connected (step S5 in FIG. 4).

On the other hand, the fault detecting unit 30 b (FIG. 2) of the otheraccess point Pb detects the occurrence of the fault in the access pointPa based on the beacon information Iba, starts the operation of thepermission information generating unit 40 b (FIG. 2). The faultdetecting unit 30 b (FIG. 2) transmits the permission information Ip tothe client terminals Cb-Cd through the main unit 1 b (FIG. 2) (step S6in FIG. 4).

Upon receiving the permission information Ip, the transceiver units 50b-50 d (FIG. 3) of the client terminals Cb-Cd in the area Ab undercontrol of the access point Pb are set to the emergency ID receptionpermitting state (step S7 in FIG. 4).

FIG. 8 is a diagram showing connection processing in the fault occurringstate of the wireless LAN system according to the FIG. 1 embodiment. Theconnection controlling unit 70 a (FIG. 3) of the disconnected clientterminal Ca transmits the emergency ID code to the client terminal Cdthrough the transceiver unit 50 a (FIG. 3). The connection controllingunit 70 a (FIG. 3) then performs connection processing such as log-inprocessing for the client terminal Cd that was searched for during thesearch processing (step S8 in FIG. 4).

The client terminal Cd controls communication between the clientterminal Cd itself and the access point Pb and, at the same time, relaysdata to be communicated between the client terminal Ca and the accesspoint Pb (step S9 in FIG. 4).

In this way, the client terminal Cd performs as a repeater that relayscommunication data of the client terminal Ca that is a disconnectedclient terminal. In this embodiment, the equal distribution system isused and all client terminals Ca-Cd operate under the same logic.Therefore, all client terminals Ca-Cd are eligible for a repeater.

Thus, at emergency time, even if the ID code of the client terminal Cais different from the ID code of the Client terminal Cd, the emergencyID code is used for all the client terminals Ca-Cd commonly. This allowsthe client terminal Ca to connect to one of the client terminals Cb-Cd.

The fault recovery processing for the whole LAN system L is completed byexecuting the above steps.

FIG. 9 is a diagram showing another connection processing in the faultoccurring state of the wireless LAN system according to the FIG. 1embodiment. Instead of the processing shown in FIG. 8 in which theclient terminal Ca connects to the access point Pb through the repeatcontrolling unit 80 a of the client terminal Cd (steps S8 and S9 in FIG.4), the client terminal Ca obtains communication information from theclient terminal Cd. This communication information includes informationon the access point Pb to which the client terminal Ca can access. Then,the search controlling unit 60 a and the connection controlling unit 70a of the client terminal Ca negotiate directly with the access point Pbto connect the client terminal Ca thereto (steps S18 and S19 in FIG. 4).

This method prevents the communication load from being concentrated atthe client terminal Cd, thus minimizing a decrease in the throughput ofthe wireless LAN system Ll.

In the above embodiments, each of the access points Pa and Pb consistsof the main unit 1 a or 1 b, fault detecting unit 10 a or 10 b,disconnection controlling unit 20 a or 20 b, fault detecting unit 30 aor 30 b, and permission information generating unit 40 a or 40 b,respectively. Instead of this configuration, the units except the mainunit 1 a and 1 b may be implemented by a software program built in theaccess points Pa and Pb. As shown in FIG. 2, this software program isstored on a recording medium 96 a or 96 b, such as a memory contained inthe access point Pa or access point Pb. Processing means 97 a or 97 b,such as the CPU (Central Processing Unit), is provided to read thisprogram for execution.

On the other hand, each of the client terminals Ca-Cd consists of eachof the transceiver units 50 a-50 d, each of the search controlling units60 a-60 d, each of the connection controlling unit s70 a-70 d, and eachof the repeat controlling units 80 a-80 d, respectively. These unitsexcept the transceiver units 50 a-50 d may be implemented by a softwareprogram built in each of the client terminals Ca-Cd. As shown in FIG. 3,this software program may be stored on each recording medium 98 a-98 dsuch as a memory contained in each client terminal Ca-Cd. Eachprocessing means 99 a-99 d, such as the CPU, is provided to read thisprogram for execution.

Even when a fault occurs in an access point, the system according to thepresent invention eliminates the need for a client terminal connected tothat access point to wait until another access point transmits beaconinformation. Instead, the client terminal automatically searches foranother nearby client terminal and causes the nearby client terminal toperform as a repeater. This allows management information required forcommunication control to be obtained easily and quickly. As a result,communication among client terminals may be reestablished more quicklythan in the conventional examples described above.

In addition, the system according to the present invention prevents aplurality of client terminals with no connection destination fromattempting to connect to the same access point at the same time. Thisaccess-point load balancing ability prevents the throughput of the wholeLAN system from being decreased.

1. A wireless local area network system comprising a plurality of accesspoints and a plurality of client terminals; wherein each of saidplurality of access points comprises: a main unit for communicating withsaid client terminals, a first fault detecting unit for detecting afault on said main unit, and a disconnection controlling unit fordisconnecting said client terminal connected to said access point wheresaid fault was detected by said first fault detecting unit; and whereineach of said plurality of client terminals comprises: a transceiver unitfor communicating with said access point, a search controlling unit forsearching for another client terminal to which said client terminaldisconnected from said access point is to be connected, and a connectioncontrolling unit for connecting said disconnected client terminal tosaid searched client terminal by said search controlling unitindependent of the plurality of access points.
 2. The wireless localarea network system as defined in claim 1, wherein each of said clientterminals further comprises a repeat controlling unit for controllingcommunication between said disconnected client terminal and one of saidaccess points connected to said searched client terminal.
 3. A faultrecovery method for use in a wireless local area network systemcomprising a plurality of access points and a plurality of clientterminals, the method comprising the steps of: detecting, by each ofsaid access points, whether a fault occurs on each of said access pointsitself; disconnecting, by said access point which has detected saidfault, said client terminal connected thereto; searching for, by saiddisconnected client terminal, another of said client terminals to whichsaid disconnected client terminal is to be connected; and connectingsaid disconnected client terminal to said searched client terminalindependent of the plurality of access points.
 4. The fault recoverymethod for use in a wireless local area network system as defined inclaim 3, further comprising the step of controlling, by said searchedclient terminal, communication between said disconnected client terminaland another of said access points connected to said searched clientterminal.
 5. A recording medium storing therein a computer program forexecuting a fault recovery process for use in a wireless local areanetwork system comprising a plurality of access points and a pluralityof client terminals, the process comprising the steps of: detecting, byeach of said access points, whether a fault occurs on each of saidaccess points itself; disconnecting, by said access point which hasdetected said fault, said client terminal connected thereto; searchingfor, by said disconnected client terminal, another of said clientterminals to which said disconnected client terminal is to be connected;and connecting said disconnected client terminal to said searched clientterminal independent of the plurality of access points.
 6. The recordingmedium storing therein a computer program for executing the faultrecovery process for use in a wireless local area network system asdefined in claim 5, further comprising the step of controlling, by saidsearched client terminal, communication between said disconnected clientterminal and another of said access points connected to said searchedclient terminal.